Electrochemical vs. Photometric Detection

Electrochemical vs. Photometric Detection in [Diabetic Test Strips](/sell-diabetic-supplies/)

Test strips switched from reading a color change (photometric detection) to reading an electrical signal (electrochemical detection) decades ago. The first electrochemical meter for self-monitoring was the pen-sized ExacTech, which MediSense launched in 1987 [3]. By 2010 most glucose biosensors were electrochemical [3]. Clarke and Foster's history of blood glucose meters traces the four decades of design changes behind that shift [2].

Photometric Technology

Photometric strips measure color. Glucose reacts with an enzyme on the strip pad and the pad changes color. A meter called a reflectometer then measures the light the pad reflects [3]. Dextrostix, the first blood glucose strip, appeared in 1965. The Ames Reflectance Meter that read it followed in 1971 [3]. Early photometric systems had clear limits:

• They needed larger blood samples (more than 3 µL).
• Dirt on the optics and ambient light could interfere with the reading.
• They were slow. With Dextrostix, blood sat on the strip for one minute and was washed off before the strip went into the meter [3].

Electrochemical Technology

Electrochemical strips turn the enzyme reaction into an electrical signal [1][3]. The enzyme takes electrons from glucose, and a mediator (a helper chemical such as ferrocene or ferricyanide) carries them to an electrode printed on the strip [3]. Mediators replaced oxygen in that job, so these strips avoid the "oxygen deficit" that limited first-generation sensors [3].

The meter then reads the signal one of two ways. OneTouch Verio and Accu-Chek Aviva Plus strips are amperometric: the meter measures the current [5][6]. FreeStyle Lite strips are coulometric: the meter measures the total charge released over the reaction time [4].

The FDA decision summaries for three major-brand strips give concrete numbers:

• Sample size: FreeStyle Lite needs 0.3 µL of blood and OneTouch Verio needs 0.4 µL, while Accu-Chek Aviva Plus needs 0.6 µL [4][5][6].
• Speed: each of those three strips lists a 5-second test time [4][5][6]. Yoo and Lee's 2010 table of commercial meters showed 4 to 8 seconds, so a result in under 5 seconds wasn't the norm then either [3].
• Maintenance: with no optics to keep clean, electrochemical meters need little upkeep [3]. They still have interferences of their own. Hematocrit (the share of blood made up of red cells) causes the largest errors, and ascorbic acid (vitamin C) can be oxidized at the electrode and push a reading up [3].

Market Dominance

Electrochemical strips took over self-monitoring of blood glucose (SMBG) on performance and price. Yoo and Lee's 2010 review credits their sensitivity and reproducibility. It also names easy maintenance and low cost as reasons [3]. In that review, most point-of-care strips were disposable screen-printed electrode strips made of plastic or paper [3]. All three FDA decision summaries we checked describe an electrochemical method: amperometry for Verio and Aviva Plus, coulometry for FreeStyle Lite [4][5][6].